1. Field of the Invention
The present invention relates to a hot-gunning method for repairing converters.
An object of the present invention is to provide an epochal hot-gunning method for repairing converters for extending the life of the lining bricks and for reducing the original amount of the material to be gunned.
2. Description of the Prior Art
Recently the life of the lining of a converter is not only determined by the durability of the lining bricks but is also greatly influenced by the slag control (a steel producing method wherein the basicity of the slag is adjusted in the refining step) and the use of a material to be gunned or baked onto the lining bricks.
Particularly, the amount of the material to be gunned used has increased so quickly as to approach the original unit of bricks today.
Generally, the mechanism by which the gunned material is deposited on the lining bricks is presumed to be that a deposited layer of the gunned material physically adheres first to the lining brick surface (internal surface of the converter), reacts by furnace heat or the like to be sintered with the lining brick surface, and is further made to react also with various compounds of the slag to form a strong hard sintered layer.
Generally, however, since the conventional material to be gunned contains 15 to 20% by weight water, there are defects created at the time that the gunned material physically adheres to the lining bricks. Because of the high temperature of the furnace, the water in the gunned material is gasified and expands so quickly that the bonding force is impaired and the gunned material peels off early during the work and will not perform its inherent function very well.
In order to solve such problems, there have been already suggested inventions mostly to improve the binder. For example, a hot-gunning refractory material is mentioned in the publication of Japanese Patent Laid Open No. 26206/1973, a refractory composition is mentioned in the publication of Japanese Patent Publication No. 27049/1967, a method of hot-repairing furnace walls of converters and the like is mentioned in the publication of Japanese Patent Laid Open No. 127413/1977 and a dry hot-repairing gun material is mentioned in the publication of Japanese Patent Laid Open No. 154818/1977. However, these compositions have not yet perfectly solved the above described problems.
The invention of the refractory composition mentioned in the publication of Japanese Patent Publication No. 27049/1967 is made of a refractory composition (mostly a material to be gunned) consisting of substantially non-acid refractory granules, 2 to 12% of solid pitch granules having a softening point of at least 200.degree. F. (about 933.degree. C.) and having such a granule diameter that substantially all the amount passes through a 4-mesh sieve and a substantial amount is retained on a 100-mesh sieve, 0.05 to 4% of a plasticizer and 0.5 to 5% of a water-soluble cold setting bonding component. However, there are defects in that the solid pitch is so comparatively fine that it is melted by the furnace heat within a very short time and therefore the gunned material deposited on the furnace wall will flow away together with the molten pitch before being sintered.
Furthermore, the method of hot-repairing furnace walls of converters and the like mentioned in the publication of Japanese Patent Laid Open No. 127413/1977 relates to a method wherein refractory granules, which are covered on the surfaces thereof with a high melting point pitch have less than several % of a pitch of the same quality granulated to a diameter of 0.3 to 2.0 mm added and mixed, are gunned by means of a normally used dry-gun. However, there are defects in that the required steps of covering the granules with the pitch and granulating the pitch are complicated and thus elevate the cost.